Wednesday, May 7, 2014

New paper finds substantial portion of Arctic warming is natural, not due to man-made CO2

A paper published today in Nature finds NE Canada and Greenland warming since 1979 is largely due to natural variability of ocean oscillations rather than anthropogenic climate change. According to the authors, "We find that the most prominent annual mean surface..warming in the Arctic since 1979 has occurred in northeastern Canada and Greenland. In this region, much of the year-to-year temperature variability is associated with the leading mode of large-scale circulation variability in the North Atlantic, namely, the [natural] North Atlantic Oscillation. Here we show that the recent warming in this region is strongly associated with a negative trend in the North Atlantic Oscillation" and "a substantial portion of recent warming in the northeastern Canada and Greenland sector of the Arctic arises from unforced natural variability" rather than anthropogenic climate change. Climate alarmists claim Arctic warming is the canary in the mine where "evidence" of man-made climate change is most apparent, but this paper and many others demonstrate much of the "climate change" in the Arctic is simply due to natural variability, and not unusual in comparison to many rapid Arctic warming episodes in the past.

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Rapid Arctic warming and sea-ice reduction in the Arctic Ocean are widely attributed to anthropogenic climate change1, 2, 3. The Arctic warming exceeds the global average warming because of feedbacks that include sea-ice reduction4, 5 and other dynamical and radiative feedbacks6, 7, 8, 9, 10, 11, 12, 13. We find that the most prominent annual mean surface and tropospheric warming in the Arctic since 1979 has occurred in northeastern Canada and Greenland. In this region, much of the year-to-year temperature variability is associated with the leading mode of large-scale circulation variability in the North Atlantic, namely, the North Atlantic Oscillation14, 15. Here we show that the recent warming in this region is strongly associated with a negative trend in the North Atlantic Oscillation, which is a response to anomalous Rossby wave-train activity originating in the tropical Pacific. Atmospheric model experiments forced by prescribed tropical sea surface temperatures simulate the observed circulation changes and associated tropospheric and surface warming over northeastern Canada and Greenland. Experiments from the Coupled Model Intercomparison Project Phase 5 (ref. 16) models with prescribed anthropogenic forcing show no similar circulation changes related to the North Atlantic Oscillation or associated tropospheric warming. This suggests that a substantial portion of recent warming in the northeastern Canada and Greenland sector of the Arctic arises from unforced natural variability.